Hi I’m Alex McColgan, and you’re watching Astrum, and today I am super excited.
Why?
Because I get to show you the amazing planet that is Saturn.
As far as the planets go, this is my favourite that isn’t Earth.
And I think by the end of this video, you may agree with me, because thanks to the Cassini
probe, we have some astonishing imagery of this beautiful planet.
I’m going to give insights to these pictures, as well as explain everything you could want
to know about the 6th planet from the Sun.
Physical Characteristics Saturn is big.
It’s is a gas giant with an average radius about nine times that of Earth, making it
the second biggest planet in our Solar System.
I say average radius though, because its equatorial and polar radii differ by almost 10%: 60,268
km at the equator, versus 54,364 km from pole to pole.
While only one-eighth the average density of Earth, 0.687 g/cm3 compared to 5.514 g/cm3,
with its larger volume Saturn has the mass of over 95 Earths.
Interestingly, Saturn is the only planet of the Solar System that is less dense than water—about
30% less.
Saturn is classified as a gas giant because the part of the planet we see is just gas,
it doesn’t have a surface that we know of, although it may have a solid core.
Saturn is called a gas giant, but it is not entirely made of gas, it’s just got too
much mass for that.
Especially when we know that it consists primarily of hydrogen, which becomes liquid under high
pressures.
Saturn has a very hot interior, reaching 11,700 °C at the core which is twice as hot as the
surface of the Sun, and the planet radiates 2.5 times more energy into space than it receives
from the Sun.
If we look at Saturn through the infrared, we see Saturn's glow, represented in brilliant
shades of electric blue, sapphire and mint green.
On the night side (right side of image), with no sunlight, Saturn's own thermal radiation
lights things up.
This light is generated deep within Saturn, and works its way upward, eventually escaping
into space.
Scientists predict that Saturn's interior is probably made of a core of iron, nickel
and rock, surrounded by a deep layer of metallic hydrogen, a middle layer of liquid hydrogen
and liquid helium and an outer gaseous layer.
But seeing as we can’t even land on the surface of Venus for any extended period of
time without being crushed, actually testing this theory for Saturn where pressures and
gravity are huge is a bit of a ways off.
Atmosphere Saturn's atmosphere has a banded pattern similar
to Jupiter's, but Saturn's bands are much fainter and are much wider near the equator.
And the reason Saturn is yellow?
It has ammonia crystals in its upper atmosphere.
But while the surface of Saturn may appear calm, the planet is actually very active.
The winds on Saturn are the second fastest among the Solar System's planets, after Neptune's.
They can be a blistering 1800 km/h.
Visible storms are also known to appear on Saturn, like this one that lasted just under
a year in 2011.
Every 30 Earth years, the planet produces what is called a “Great White spot” which
is a unique but short-lived phenomenon that occurs once every Saturnian year.
If this storm wasn’t an early rendition of this great white spot, the next one is
expected in 2020.
In storms on Saturn, lightning is produced.
Cassini has even detected the sound of the thunder.
But while this mean sound weak, the power of lightning on Saturn is about 1,000 times
stronger than on Earth.
Poles Still talking about storms, but moving on
to the planet’s poles, we find that each pole has giant, permanent storms.
NASA reported in November 2006 that Cassini had observed a "hurricane-like" storm locked
to the south pole that had a clearly defined eyewall.
Eyewall clouds had not previously been seen on any planet other than Earth.
The ring is similar to the eyewall of a hurricane, but much larger.
The clear air there is warm, like the eye of hurricane, but on Saturn it is locked to
the pole, whereas a hurricane on Earth drifts around.
The north pole is even more unusual.
There is a persistent hexagon shaped storm that rotates with the planet, but it doesn’t
change longitude like the rest of the cloud on the planet.
The straight sides of the polar hexagon are each about 13,800 km (8,600 mi) long, making
them larger than the diameter of the Earth.
And why does this happen and to such a big scale?
No-one really knows.
Nature seems to have a thing for 60 degree angles though.
Giant’s Causeway anyone?
But like the south pole, the north pole also has a vortex, or eye wall.
Aurora While not anywhere near as strong as Jupiter’s,
Saturn does have a magnetosphere which is strong enough to deflect Solar wind from the
Sun.
And Saturn's magnetosphere, like Earth's, produces aurorae.
Their location and brightness strongly depends on the Solar wind pressure: the aurorae become
brighter and move closer to the poles when the Solar wind pressure increases.
The same process produces auroras on both Earth and Saturn: electrons stream along the
magnetic field lines into the upper atmosphere.
There, they collide with atoms and molecules, exciting them to higher energies.
The atoms and molecules release this added energy by radiating light at different colours
and wavelengths.
On Earth, this light is mostly from oxygen atoms and nitrogen molecules.
On Saturn, it is from hydrogen.
Rings The rings for me are one of the highlights
of the planet.
Saturn has a prominent ring system that consists of nine continuous main rings, made mostly
of ice particles with a smaller amount of rocky debris and dust.
While they are mainly named after letters of the alphabet, the naming conventions are
still a little confusing so bear with me.
The first 5 rings, from the closest to the planet outward are, D ring, which is very
faint, C ring, B Ring – which is the brightest and widest of all the rings, A ring – which
is the last of the large bright rings, and then F ring.
The rings extend from 66,000 km to 120,700 km above Saturn's equator are made up mostly
of water ice, with traces of rocks.
If we look in the ultraviolet at a section of the brightest rings, it shows there is
more ice toward the outer part of the rings, than in the inner part.
The red in the image indicates sparser ringlets likely made of 'dirty,' and possibly smaller,
particles than in the icier turquoise ringlets.
If we look at a picture representing radio occultation, we can judge the size of the
individual particles that made up the rings.
Color is used to represent information about ring particle sizes based on the measured
effects of the three radio signals.
Shades of red indicate regions where there is a lack of particles less than 5 centimeters
(about 2 inches) in diameter.
Green and blue shades indicate regions where there are particles of sizes smaller than
5 centimeters (2 inches) and 1 centimeter (less than one third of an inch), respectively.
Overall it’s thought that the particles in the rings aren’t bigger than 10m, and
can be microscopic in size.
Using occultations again, scientists observe the brightness of a star as the rings pass
in front of the star.
This provides a measurement of the amount of ring material between the spacecraft and
the star which means we can estimate how thick the rings are.
Colors in this image indicate the orientation of clumps, and brightness indicates the density
of ring particles.
Yellow is too dense to let starlight through, and so shows this to be the densest parts
of the main rings.
The main rings are thought to be as little as 10m thick, to 1 km thick.
Particularly the B rings, we can see that the rings are not perfectly symmetrical.
During the planet’s equinox, the rings can get a bit wonky.
Look at the top of this video, where the B ring meet the A ring.
Zooming in on this structure reveals ridges and spokes a couple of km tall, their presence
given away by their shadows.
Zooming out again, we can see the scale of how many spokes there are during this period.
Oscillations happen all the time in the rings though, perhaps due to the presence of a shepherd
moon, or even just naturally.
The differences, which can be seen all in only a day, can be up to 200km.
So I’ve talked about the d, c, b, and a rings, and also mentioned the F ring.
The F ring has a great can also get quite wonky, and has a perfect example of what is
called a shepherd moon, Prometheus, that leaves a ripple in the ring as it orbits.
Once during its 14.7-hour orbit of Saturn, Prometheus (102 kilometers, or 63 miles across)
reaches the point in its elliptical path, called apoapse, where it is farthest away
from Saturn and closest to the F ring.
At this point, Prometheus' gravity is just strong enough to draw a "streamer" of material
out of the core region of the F ring.
So what comes after the F ring?
First, Janus or Epimetheus Ring, G Ring, Pallene Ring and then the E Ring.
Now, this picture is amazing, and I might do a separate video just on this.
But for the sake of time, this bright blue ring is the E ring, you can just about see
the faint Pallene Ring at the top of the picture.
The G ring is the next distinct ring, and again you can just about see the Janus or
Epimetheus ring at the top below it.
And can you see us?
We’re all in this picture too.
Here’s Earth and the Moon!
So now you know about the rings.
I think you’ll agree they are so interesting in their own right.
Theories abound as to why they are there, but simply we don’t know.
We know that some of the moons are responsible for some of the material there, and we also
know that some of the material there is responsible for some of the moons.
Moons And talking of moons, I’m going to give
you a brief run down about those that belong to Saturn.
Again, I plan to do a separate video or videos about them as there are at least 150, 53 with
formal names!
They come in all shapes and sizes, and most uniquely, Saturn’s biggest moon Titan, which
is even bigger than Mercury, is the only moon in the Solar System with a thick atmosphere
around it.
I’m also going to throw in here that Saturn has the Death Star orbiting it, biding its
time.
We call it Mimas.
Orbit Lastly, I’m going to talk about Saturn’s
orbit.
Now Saturn orbits about 9 to 10 times further away from the Sun as Earth, and one year on
Saturn takes 30 Earth years.
Funnily enough, a day on Saturn is different depending on where you stood (not that you
could stand on Saturn).
At the equator or at the poles, a day lasts about 10 hours and 14 minutes.
Everywhere else (apart from the poles) a day lasts 10 hours and 38 minutes.
The issue is, because Saturn isn’t solid, it’s not bound to rotate at the same speed
all over.
Saturn Colours I just want to leave you with this.
Few sights in the solar system are more strikingly beautiful than softly hued Saturn embraced
by the shadows of its rings.
The gas planet's subtle northward gradation from gold to azure is a striking visual effect
that scientists don't fully understand.
Current thinking says that it may be related to seasonal influences, tied to the cold temperatures
in the northern (winter) hemisphere.
And despite all that we have learned from Cassini, Saturn remains a world
of mystery.